Terrazzo floors and panels are used extensively today for architectural purposes. Terrazzo floors date from early neolithic buildings (9.000-8.000 BC) in Western Asia, such as in Turkey. Other sites with early neolithic terrazzo floors have been found in the eastern Mediterranean. The neolithic terrazzo floors were constructed of burnt lime, crushed limestone, and clay, colored red with ochre, and polished. The embedded crushed limestone gives these terrazzo floors a slightly mottled appearance. Interestingly, the production of burnt lime for these early terrazzo floors predates the firing of pottery by almost a thousand years. These floors are almost impenetrable to moisture and are very durable, but their construction involved a high input of heat energy to produce the burnt lime.
In the 1400s terrazzo reappeared as a low cost flooring material. Marble chips were set in clay. Goat milk was used as a sealer. In the 1800's portland cement started to be used in Terrazzo. Installation of Terrazzo became much easier and more extensive after the introduction of electric industrial grinders and other power equipment in the twentieth century. It was a very popular finish in the 1930's 1940's and the 1950's. Examples are the side walks along the beach front in Rio De Janiro and the large theaters and restaurants build between the late 30s and late 50s in the United States.
Today, exterior terrazzo floors are usually constructed by embedding marble chips and other aggregate in concrete and then exposing the marble chips and other fine aggregates on the surface of finished concrete or by grinding and polishing the concrete surface. Much of the preliminary work of terrazzo fabrication involves the laying of traditional concrete pad and flooring. The method is time driven. Conventional marble-chip, cementious terrazzo, rustic terrazzo, requires three layers of materials. First, a solid, level concrete pad or flooring foundation, 3 to 4 inches thick, is laid. Before the concrete has set up, the concrete surface is raked to give the surface bite for the next step. Then, and before the concrete has set up, a 1-inch layer of sandy concrete topping is applied to the raked concrete surface. For the final layer, a mixture of cement and fine aggregate is blended and placed on the top of the concrete mortar topping layer before it sets up to from a surface layer. While this surface layer is still wet, additional aggregate is broadcast on the surface to insure adequate coverage and uniform density of chips. A lightweight roller is then rolled over the entire surface to give a flat surface. When design elements are incorporated in the terrazzo finish, the different color mixtures of concrete and aggregate are prepared and then applied over the mortar topping layer in prescribed sections to create the design. Then matching aggregate is hand seeded into the different sections to achieve a uniform density of aggregate and color. Terrazzo design flooring is very labor intensive.
In addition to marble aggregate blends, other aggregate blends can be used such as colored rock or pebbles, recycled glass, shaped metal, like bolts and screws, and medallions, can be used in terrazzo. However when metal particles are used, corrosion resistant metals, such as bronze, stainless steel must be used to prevent staining and/or corrosive destruction. Reactive metals, like steel, expand when corroded and break up the terrazzo.
When the rustic terrazzo is thoroughly dry, the upper surface is ground with a terrazzo grinder to give a smooth even finish. The surface is then cleaned, polished with a terrazzo polisher, and/or sealed.
A major limitation to exterior cementious terrazzo is that it can only be applied to a fresh, new, clean concrete surface, i.e. the raked concrete surface of a new pad or flooring. The installation of exterior cementious terrazzo on the surface of an existing concrete pad or flooring has not been successful. Cracking and delamination are common problems. Because of such problems, most construction companies will refuse to apply terrazzo over an existing concrete surface, or will refuse to furnish a warranty for a terrazzo finish over an existing concrete surface.
In addition, although terrazzo is ideally suit to create complex designs in surfaces, such designs require careful application of the final layer and the seeding of the various aggregates to keep sharp boundaries between design elements and insure that different colored aggregate to do cross over to adjacent elements of the design. Frequently saw cuts are used to sharpen and demark boundaries between design elements.
Rustic terrazzo fabrication require at least 24 hours of set up time before it can be safely subject to foot and light traffic and at least 72 hours before it can be subject to vehicle and heavy traffic. Maximum strength for concrete is reached in 28 days.
It is an object of the present invention to provide a process to apply a terrazzo finish to an existing horizontal concrete surface with an insignificant thickness and weight penalty. Thus, the present method permits the application of a terrazzo finish to an existing concrete structure and does not require the laying of a new concrete pad or floor. Thus, for example, an existing mall concrete flooring can be refinished without the need to lay a brand new 3 to 4 inch concrete pad over the existing concrete floor or demolishing the existing concrete flooring to install the new concrete flooring. When a second pad is applied all over an existing pad, door threshold have to be adjusted. Frequently structural limitations will not permit the laying of a second concrete pad over an existing concrete pad or floor because of the added weight.
It is a further object of the present invention to provide a method applying a terrazzo without time constraints. In other words, the present method does not require the laying down of three layers of cementious material before they have set up as required in the rustic terrazzo method.
It is an additional object of the present invention to provide a terrazzo finish that can be subject to foot and light traffic four hours after application and to vehicle and heavy traffic six hours after application. Thus, for example, an exterior or interior mall can be resurface in terrazzo at night when the mall is closed and open to traffic the next morning after 4 or 6 hours as the case may be for light traffic or heavy traffic.
It is a further object to provide a process for apply a terrazzo finish to a horizontal surface that can accomplish the desired result in a minimum amount of time and with an efficient use of labor.
It is another object of the present invention to provide a terrazzo process that allows the design in a terrazzo finish to be made in a single step without the need to first render the design with the application of a mixture of aggregate and cement to form the final layer and then secondly seed the final layer with additional aggregate to made the aggregate density and color uniform. Both these steps are labor intensive.